My M21 16ga is a Trap grade but not a Trap gun, and it's reverse choked with Mod in the right and Cyl in the left. When I got it the triggers had been reversed and since they were not re-bent they stuck out funny. Somebody really wanted the front trigger to fire the open barrel. They were simple to switch back to original, the letter on the gun lists grade, stock dimensions and the individual for whom it was made but nothing about chokes.